It is known that an Ethernet bus type communication network operates according to the CSMA/CD mode, in other words, by carrier sensing with collision detection. Some research work has proposed the use of priority allocation mechanisms implemented in the Ethernet packets to enable, in this type of communication network, data streams to be transmitted over the Ethernet bus. However, this type of priority allocation mechanism is intended more for computer networks organized around routers. It is not suited to small communication networks of the domestic network type in which the elements are passive.
The object of the invention is to propose a mechanism for reserving, on at least one node of an Ethernet bus type communication network, a certain fraction of the bus bandwidth so as to enable a data stream to be transmitted, for example, an audio/video stream according to the DVB (Digital Video Broadcast) standard.
The idea on which the invention is based is to superimpose on the communication protocol of a digital bus, bus access arbitration by the circulation of a token between the nodes of the network so as to be able to control the times of write mode access to the bus by the nodes of the network. The term token denotes a write permission which is granted to a node of the network in the sense of a so-called token-ring network. The bandwidth is divided into cycles during which the write permission of the token passes from one node to another according to a predetermined and reproducible strategy over a number of cycles.
The document “Rether: A Real-Time Ethernet Protocol” by Chitra VENKATRAMANI, published in November 1996, describes a network consisting of nodes having a permission to send during a time slot dependent on the previously reserved bandwidth. A control node divides up the bandwidth temporally by creating a first list of nodes having requested bandwidth, and a second list of nodes not having reserved. During a cycle, the terminals of the first list send their messages first, then the terminals of the second list have their turn during the remaining time. When the end of the cycle occurs, the message transmissions by the nodes of the second list are stopped and resume on the next cycle at the point at which they were interrupted in the second list. In this document, not all the terminals are sure to be able to have their turn during a cycle.